Quick-fit anti-skid system for vehicle wheels and associated device for fixing to the wheel

ABSTRACT

An anti-skid system for vehicle wheels includes gripping elements which are intended to make contact with the tread of the wheel and are arranged at the free ends of arms joined to a central connecting body, a clamping element ( 15 ) apt to be fastened to the rim of the wheel, and a constraining assembly able to establish a connection between the arms ( 21, 22 ) and the clamping element ( 15 ), the arms ( 21, 22 ) being in the form of flexible laminar strips and the constraining assembly including at least one linear traction member ( 30 ) which is non-extendable, but adjustable lengthwise; an advantageous clamping element ( 15 ) which makes the system more cost-effective and mounting thereof on the wheel more convenient is also described.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an anti-skid system for vehicle wheels,in particular a system with radial support elements, which is intendedto be placed on the wheel of a vehicle and positioned automatically onthe tire upon the first revolutions during movement of the vehicle. Theinvention also relates to a device for fixing this system, apt to beclamped onto a bolt of the wheel rim.

Some known anti-skid systems are described in EP-496,702 and CH-689,206,which are regarded as incorporated herein by way of reference.

In these known devices, four radial support elements of a snow-chainconverge towards a central connecting body. The latter is thenresiliently fastened in various ways to a system ensuring constrainingto a bolt of the wheel rim.

In these systems, moreover, it is provided that the fixing mechanism tothe bolt of the rim is in the form of a bush-like body through which theconstraining system is fitted.

The bush is composed of a jaw-like arrangement which can be clamped ontothe bolt by screwing a liner onto a deformable internal body. The bushis fixed onto the bolt of the rim by way of a preliminary operationbefore mounting the whole anti-skid system onto the wheel. Since,however, this operation must be performed with the aid of a tool and issomewhat difficult, normally it is performed at the start of the winterseason and the bush is then left for a long period of time mounted onthe vehicle rim, with the drawbacks which can be imagined. Followingthis operation, at need (for example in the case of snow on the road),the motorist must attach to the bush the remaining portion of theanti-skid system, which is that intended to provide the tire withadequate grip to the slippery road surface.

In addition to the difficulty mentioned above there is a further problemassociated with the arrangement of the bush. Since tightening onto thebolt is performed by means of partial deformation of the internalelement of the bush, obtained through helical coupling of thescrew/female thread type, it is not possible to achieve a goodtightening action on a wide variety of bolts of varying sizes.Consequently, it is required to envisage a specific bush (also called“fix” in the technical jargon) for each bolt size. This means that,during purchase, the user must find out the bolt size on his/her vehicleand supply this information to the sales outlet so that they can providethe right equipment. As can be imagined, this procedure is inconvenientand may be a source of errors both for the sales outlet (who among otherthings must keep a larger number of articles in stock) and for thepurchaser.

Moreover, some users may encounter difficulties at the time of mountingthe actual anti-skid system onto the bush previously fastened to thebolt. In fact, with one hand it is required to keep the anti-skid systempositioned and pressed against the tire of the wheel while, at the sametime, with the other hand a coupling lever or cotter pin must be engagedwith the bush already mounted on the bolt and situated behind the radialsupport elements.

SUMMARY OF THE INVENTION

The object of the present invention is therefore that of overcomingthese drawbacks and providing an anti-skid system, mounting of which iseven easier than that of the devices already proposed.

A further object of the invention is to provide a fixing bush orclamping element which can be easily fastened to and removed from thewheel bolt and which is available as a single, sufficiently low-cost kitwhich can be adapted by the final user to the specific bolt of the rim.

A further object of the invention is to provide a further improvedfixing bush which can be fastened, without any modification, to boltswithin a wide range of sizes.

The abovementioned objects are achieved, according to the invention, byan anti-skid system.

In particular, the anti-skid system according to the invention thus nolonger has any resilient element arranged between the rim and theconnecting body for exerting a pulling force on the system. This pullingand/or tensioning force is obtained, instead, by using arms with asuitable shape and elasticity which are tensioned by means of anadjustable constraining device consisting of a non-extendable lineartraction member, such as a chain or a cable, which joins theconstraining lever to a connecting body of the arms which is designedwith a suitable structure.

According to an important aspect of the invention, moreover, theclamping device, which is intended to be removably fixed onto the wheelbolt, has an external body, a removable internal body as well as anoperating member, which are configured and coupled together in such away as to make the fixing and removal operation much easier.

According to another aspect, the internal body is not removable, but isconfigured in such a way as to be universally applicable to a wide rangeof bolts of various sizes.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristic features and advantages of the system accordingto the invention will nevertheless appear more clearly from the detaileddescription which follows of some preferred embodiments thereof,provided by way of example and illustrated in the accompanying drawings,in which:

FIG. 1 is a side elevation view, partly sectioned, of a vehicle wheelequipped with a system according to the invention;

FIG. 2 is a partial front elevation view of the connecting body of thesystem according to FIG. 1, in the direction of the arrow II;

FIG. 3 is a partial sectional view of an alternative embodiment of theconnecting body according to FIG. 2;

FIG. 4 is a front elevation view of FIG. 3;

FIGS. 5A, 5B and 5C are, respectively, a top plan view, front elevationview and longitudinal section view along the line V-V of an alternativeembodiment of the connecting body according to FIG. 2;

FIGS. 6A and 6B are, respectively, a top plan view and front view whichshow in detail the constraining element in its entirety fastened to thebolt of a vehicle wheel;

FIGS. 7A and 7B are, respectively, a partially sectioned side elevationview and front elevation view of a preferred embodiment of the clampingelement according to the invention; and

FIGS. 8A, 8B to 13A, 13B are, respectively, views similar to those ofFIGS. 7A and 7B of further embodiments of the clamping element.

DESCRIPTION OF SOME PREFERRED EMBODIMENTS

As can be seen in the cross-section of FIG. 1, a vehicle wheel comprisesa tire 11 and a rim 12 provided with fixing bolts 13 which connect therim to the axle of the vehicle. A constraining assembly 14, which willbe described in greater detail below, is mounted in a removable manneron one of the bolts 13 of the wheel.

The constraining assembly 14 comprises a clamping element 15 which isintended to clamp the bolt 13 and from which there extends a threadedshank 16 which passes through a circular collar 17 supporting a couplerlever or rod 18. The coupler rod 18 is arranged eccentrically on thecollar 17 and extends towards the center of the wheel, extending also acertain distance beyond it. The clamping element 15 is fastened to andremoved from the bolt 13 by means of an operating member 19, such as arotating knob, operation of which will be illustrated in detail furtherbelow.

According to the invention, the rod 18 is freely slidable inside theseat of the collar 17, but cannot be completely extracted from it, forexample as a result of retaining rings 42 arranged at its ends.

Moreover, on the portion directed towards the center of the wheel, therod 18 carries on a bracket 38, which is also free to slidelongitudinally on the rod 18 and to which the end of a non-extendabletensioning member, for example the chain 30 shown in the figures, isfirmly attached.

Preferably this end of the chain 30 is constrained to the bracket 38also by means of vibration damping means 40 which are shown in the formof a ring of synthetic material and a clip 41.

At its other free end the chain 30 has a rubber piece 35 (FIG. 1) whichis intended to be hanged to a hook 36 mounted to a hinging pin 25 of theanti-skid system which will be seen further below.

The rubber piece 35 does not have the function of interacting with thechain 30 in order to perform tensioning of the system on the vehiclewheel, but simply has the function of keeping it to the wheel so that itis not free to move and strike components during rotation of the wheel.

The anti-skid system 20 also comprises two arms 21, 22 (FIG. 2) whichare arranged approximately at 90° with respect to each other when thesystem is operationally mounted on the wheel. The actual anti-skidcomponent, for example four plates 23 provided with spikes 24 andconnected to chain sections (not shown), is fastened to each end of thearms 21, 22.

This part of the anti-skid system will not be described in greaterdetail in this application since it is understood that its componentsare known to the person skilled in the art and for example are describedin CH-689,206.

The arms 21 and 22 are preferably formed by resilient, metal, laminarstrips and are mounted rotatably at their center on a central connectingbody 26 which may be made of metal or sufficiently rigid plasticmaterial.

The two arms 21 and 22 are for example supported on a circular race ofthe body 26 and are separated by a thin clip-like spacer 28, such as anelastic ring.

The arms have the singular shape clearly shown in FIG. 1, namelycomprising an elbow portion which is intended to be arranged in contactwith the rim 12 when the system is tensioned making use of the inherentelasticity of the arms.

The connecting body 26 has a generally flared shape and is provided atthe centre with a hole 29 through which the chain 30 is intended topass. The flared connecting body 26 has, at its inlet mouth, a series offour grooves 31, 32, 33 and 34 (FIG. 2) which are situated at about 90°with respect to each other; the grooves are intended to receive edgewisea link of the chain 30 so as to prevent it from coming out whentensioned.

Now that the overall structure of the system according to the inventionhas been described, the operating principle thereof can be easilyunderstood.

Firstly, the constraining assembly 14 is fixed onto a bolt of the wheelrim by suitably operating the tightening knob 19. This operation may beeasily performed also using both hands.

Then, in a conventional manner, the remaining portion of the anti-skidsystem is brought up to the wheel, causing the actual snow-chaintogether with the associated gripping elements to hug the tire asclosely as possible. During this operation, the chain 30 remains loose.At this point pressure is applied to the connecting body 26, moving itcloser to the rim and tensioning the arms 21, 22; once the desiredposition has been reached, the chain 30 is taken up and tensioned andfolded back along one of the arms, inserting the connecting link intoone of the grooves 31-34 of the body 26 as to lock it in position. Inorder to prevent the remaining free portion of the chain from bangingduring the rolling movement of the wheel, the end of the chain providedwith the rubber part 35 is fastened to the hook 36.

Finally, it is possible to start again with the vehicle, allowing theanti-skid system to fit properly around the tire owing the elasticreturn force which is constantly exerted by the arms 21, 22 which areunder tension.

When it is required to remove the anti-skid system, it is sufficient torelease the chain 30 by extracting it from the groove 31 and exerting apulling force on the top part of the chain adhering to the tire, therebyfreeing the top and side areas of the chain. Then the vehicle need bemoved forward one half revolution of the wheel in order to be able toremove the system and place it back into its container.

As can be understood, the technical solution proposed is extremelysatisfactory because, on the one hand, it results in a much simplifiedassembly sequence, leaving both hands free for each operation, and, onthe other hand, by making efficient use of the elasticity of the armsalone, it avoids the use of separate resilient elements for exerting thedesired holding force. In fact, problems of wear or breakage of theseresilient parts are thereby avoided. The person skilled in the art willeasily understand that the resilient piece 35 allows fastening of theend of the chain 30 in a simple manner so that the latter is unable tostrike the sides of the vehicle wheel, but said piece is not subject toany significant degree of tension and, consequently, will never resultin any problems.

Moreover, owing to the ease of operation of the operating knob 19, it ispossible to fix and remove without difficulty the entire constrainingassembly, which may therefore be mounted only when required and not lefton the wheel rim for the whole winter season.

FIGS. 3 and 4 show a variant of the connecting body 26. As in theprevious embodiment, the central support 26 has a hole 29 through whichthe chain 30 passes. In this embodiment, however, the grooves 31-34intended to retain a link of the chain are replaced by an engagingdevice formed by a hook 45, pivoting about a pin 46 of the body 26 andjoined to an actuating lever 47.

The operating principle of the variation of the tightening devicedescribed here is extremely easy to understand. The lever 47 is keptlowered so as to move the hook 45 away from the path of the chain 30until the anti-skid system has been mounted on the wheel and the arms21, 22 have been tensioned. Then the hook 45 is inserted into a link ofthe chain 30 and the chain is slackened by that small amount needed tolock together the hook 45, the chain link and the body 26 so as toprevent further slackening and lock the chain on the body. The arms 21and 22 are thus tensioned and the system is applied against the wheel.Simple pressure of the lever 47 then allows the chain 30 to be releasedduring disassembly.

FIGS. 5A-5C show a further preferred embodiment of the connecting body.Here the flared body 260 has a single groove 340 and, in the vicinitythereof, there extends an extended portion provided with a raising lip261 also provided with a groove 341.

In this way, the chain 30 is laid down and locked always in the samedirection, but is kept raised from the underlying arm 21, 22 along asignificant portion thereof. As a result it is possible to avoid theneed for shock-absorber inserts arranged along at least one of the arms21, 22 so as to protect them against the vibrational impact with thechain which would end up damaging and impairing the surface finish.

FIGS. 6A and 6B show in greater detail a preferred embodiment of theclamping element 15 according to the invention.

A bell-shaped body 50 extends integrally with the collar 17. The wallsof the bell-shaped element 50 have an internal chamfer 51 in the regionof the inlet mouth.

The bell-shaped element 50 houses internally a sleeve 52 provided with aseries of petals (fingers) 52 a able to close together, clamping in themiddle the head of a bolt 13 or 14. Each petal (finger) 52 a has aninclined external surface intended to complementary mate with theinternal chamfered surface 51 of the bell-shaped element 50. Owing tothis design, the clamping element 15 is able to clamp the bolt 13 as theengaging action between the sleeve 52 and the bell-shaped element 51increases (namely as the sleeve moves in the opposite direction to thearrows shown in FIG. 6A).

In order to establish this relative displacement between the sleeve andthe bell-shaped element, a threaded tie-rod 16 is provided, said tie-rodbeing integral, at least in the direction of longitudinal traction, withthe sleeve 52. For example the tie-rod 16 is a threaded screw with ahead 16 a engaged in a suitable seat of the sleeve 52. At the oppositeend of the threaded tie-rod 16, beyond the collar 17, the operating knob19 is screwed.

Screwing of the knob 19 causes pulling of the screw 16 to the right andtherefore tightening of the clamping element 15 onto the bolt 13. Sincethe knob 19 has relatively large dimensions, tightening of the systemonto the bolt 13 is extremely effective.

According to a preferred embodiment, the sleeve 52 may be designed as areplaceable or interchangeable part. Between one sleeve and another, thehole for insertion of the tie-rod 16 remains identical, but thethickness of the petals 52 a changes: in this way it is sufficient toenvisage a series, for example, of three different sleeves 52 in orderto be able to use the clamping element for the whole range of bolts 13available on commercially produced vehicles. Since the sleeve 52 is anextremely simple and low-cost component, it is possible to provide thepurchaser with the complete series in the same package, without asubstantial increase in costs, thus achieving full compatibility of thesame product with a wide range of vehicles.

Finally, the angle of opening α of the inclined mating surface betweenthe inner sleeve 52 and the bell-shaped body 50—which angle is identicalfor all the different sleeves which may be provided—is chosen so as tobe able to achieve an effective tightening action, without howeverrequiring an excessive force on the part of the person who must operatethe operating knob 19. This angle α is preferably in the range of 10° to30°.

Some further preferred embodiments of the clamping element 15 will nowbe described. In the figures identical reference numbers have beenassigned to like elements.

In the first embodiment shown in FIGS. 7A and 7B, the clamping elementcomprises a central bell-shaped body 50 within which there is formed achamfer portion 3′ against which a series of independent clamping blocks4′ forming a gripping jaw are intended to slide.

As is clearly shown in FIG. 7B, the gripping jaw is preferably composedof six independent clamping blocks 4′ connected together by means ofcompression springs 5′ arranged in lateral holes 6′ provided in the twoend portions of-each clamping block.

The internal ends of the clamping blocks 4′ have spurs 7′ which aredirected towards the longitudinal central axis and against which theundercut portion of a head 8′ of a tightening screw 9′ engages. Thetightening screw 9′ has, screwed thereon, the operating knob 19 whichacts in opposition to the collar 17 (only schematically shown in thesefigures) to which the bell-shaped element 50 and the constraining rod 18are joined.

A spring 11′ is arranged between the clamping blocks and the bottom ofthe bell-shaped body 50.

According to a particular feature of the invention, moreover, theexternal retaining end of the clamping blocks 4′ has a stepped shape, ascan be clearly seen from FIG. 7A. Preferably the side surface 4 a′ ofthe stepped-shaped ends is slightly flared so as to have a radialdistance from the central axis of symmetry which decreases outwards.

The clamping element is intended to be tightened around a bolt 13 orotherwise onto a larger-size bolt 14. In fact, owing to the specificshape of the stepped ends of the clamping blocks 4′, the jaws formed bythem is able to hold adequately bolts within a wide range of sizes—atleast all those which may be envisaged on standard vehicles.

The rotation of the knob 19 causes axial displacement of the screw 9′and therefore the extraction or retraction of the clamping blocks 4′from/into the body 50 in opposition to the spring 11′.

Advantageously the anti-clockwise rotation of the knob 19 “opens” thegripper formed by the clamping blocks 4′, i.e. or releases the head 8′of the screw which moves to the left (in the figure) as a result of thebias of the spring 11′ which also pushes the clamping blocks 4′ towardsthe external portion of the body 2′, freeing the bolt; conversely, theclockwise rotation of the knob 19 causes the movement of the clampingblocks 4′ towards each other and therefore firm tightening of theclamping element 15 to the bolt.

This device is extremely simple and, as already mentioned above, may bedesigned so as to hold bolts of different widths. The various componentsmay be made, for example, of pressed metal and the holes 6′ obtained bymeans of punching.

In the embodiment shown in FIGS. 8A and 8B, instead of the holes 6′ andthe compression springs 5′, the individual clamping blocks are kepttogether by bridge-pieces made of rubber or synthetic material 10′. Saidbridge-pieces, which have a certain elasticity, are joined to theclamping blocks 4′ by means of vulcanization, gluing or mechanicalfixing.

The embodiment according to FIGS. 9A and 9B has a clamping elementcomposed essentially of the same components as the two precedingembodiments. However, in this case, the six clamping blocks 16′ of thegripper are made as one piece which has a common annular body 18′, onthe inner base of the clamping blocks, provided along the whole of itsheight with a slit 18 a′ which allows the two clamping blocks adjacentthereto to move away from and towards each other. The six clampingblocks 16′ are kept together by the annular body 18′ which has smalldimensions and therefore ensures a sufficiently elastic connection, inparticular if the metal from which it is made is chosen in a suitablemanner. This part may be made of light alloy or resilient steel.

In the embodiment shown in FIGS. 10A and 10B the six clamping blocks 4′are joined together by means of a resilient washer or Belleville washer20′ which is made of a resilient metal. This spring washer 20′ is housedinside slits 21′ formed on the inner base of the clamping blocks 4′, theabovementioned clamping blocks being able to be introduced inside thebody 2 when the retaining spring 20′ is under precompression.

In the embodiment shown in FIGS. 11A and 11B the six clamping blocks 4′are kept together by means of thin rigid clips in the form of an open Vand having the function of creating connecting bridges which also formhinging axes for each clamping blocks on the inner base thereof. Acircular expansion spring 23′ is provided at the outer portion of theclamping block and keeps the clamping blocks 4′ pushed against theannular surface 3′ of the body 50.

In the embodiment shown in FIGS. 12A and 12B, the clamping element 15has six floating clamping blocks 25′ which are hinged on a pivot-likeprojection 26′ provided at the inlet mouth of the bell-shaped body 50.The threaded shank 9′ has a head 28′ which has a frustoconical shapeable to co-operate with the inclined internal surfaces 29′ of theclamping blocks 25′.

Therefore, in this case, the slanted coupling, which allowsextraction/retraction of the clamping blocks, is provided between thehead 28′ and the clamping blocks instead of between the bell-shaped bodyand the clamping blocks.

Recall of the clamping blocks is performed by means of an expansionspring 10′ which is arranged in the outermost portion of the clampingblocks.

In the last embodiment shown in FIGS. 13A and 13B, the clamping element15 has six independent clamping blocks 35′ arranged and hinged on anordinary washer 36′ mounted on a threaded bolt 37′ which passes throughthe collar 17. A bell-shaped cylindrical wall 39′, which has a chamferedinternal wall of decreasing thickness 40′, extends from the collar 17.Finally, the set of clamping blocks 35′ positioned and hinged on thewasher 36′ is held together by means of an O-ring 42′ provided inwardlyof the washer 36′. This O-ring, in view of its location, allows theclamping blocks to be forced into the open position.

In this case, moreover, the stepped shape of the clamping blocks hasbeen pronounced so as to form a hook shape which can be clearly seen andunderstood in FIG. 13A.

It is understood that the stepped shape of the outer end of the clampingblocks may be modified in the most suitable manner. For example it ispossible to envisage also that the internal surface of this clampingblock end is shaped with three adjacent faces having a differentinclination: this would allow three different bolt sizes to beadequately gripped.

As can be understood, owing to the configuration of these latterinnovative embodiments, the system of the invention is applicable to awide variety of bolts without any component having to be replaced. Thisconstitutes an undeniable advantage for the purchaser and perfectlyachieves one of the objects mentioned in the introduction.

It is understood, however, that the invention is not limited to theparticular configurations as illustrated above, which only formnon-limiting examples of the scope of the invention, but that numerousvariants are possible, all within the reach of a person skilled in theart, without thereby departing from the scope of the said invention.

In particular, the system has been described with reference to tworesilient arms 21 and 22. It is however possible to envisage, forexample, three arms for the models useful for equipping motor vehicleswith very large wheels.

Moreover, although the chamfer angle on the bell-shaped body has alwaysbeen illustrated as diverging towards the outside, a similar operatingprinciple and design could be obtained with the chamfer convergingtowards the outside.

1. An anti-skid system for vehicle wheels, comprising: gripping elementsavailable for contact with a tread of the wheel arranged at free ends ofarms (21, 22) connected to a central connecting body; a clamping element(15) apt to be fastened to a bolt of a rim of said wheel; and aconstraining assembly able to establish a connection between said arms(21, 22) and said clamping element (15), wherein said constrainingassembly comprises: a collar (17), integral with said clamping element(15), a connecting rod (18), carrying a constraining bracket (38) andfreely slidable through said collar (17), a threaded operating pin (16)extending from the clamping element (15) passing through said collar(17), and an operating knob (19) screwable on said threaded operatingpin (16) of the clamping element (15) in opposition to said collar (17).2. The anti-skid system according to claim 1, wherein said constrainingassembly further comprises: a non-extendable chain (30) connected to aconstraining element (18) fixed to the clamping element (15) and whichpasses through said connecting body (26), the connecting body having aflared shape which is provided, at an inlet mouth of said connectingbody (26), with at least one radial groove (31, 32, 33, 34) inside saidconnecting body (26) which a link of the chain (30) may be insertededgewise so as to obtain the desired locking action.
 3. The anti-skidsystem according to claim 2, wherein the free end of said chain hasresilient fastening means (35, 36) able to keep said chain adherent tothe anti-skid system.
 4. The anti-skid system according to claim 1,wherein said arms have an elbow shape, the fold of the elbow beingintended to come into contact with the rim (12) of the vehicle wheel. 5.The anti-skid system according to claim 1, wherein the clamping element(15) has a collar (17) from which projects a bell-shaped body (50)having, at least in an inlet mouth portion, a chamfered internal surface(51) able to co-operate with a corresponding chamfered surface of aninternal sleeve (52) which can be engaged with and tightened on a bolt(13, 14) of the rim, said sleeve (52) being able to slide inside thebell-shaped body (50) actuated by said threaded pin (16) protruding fromthe collar (17) and displaced by the operating knob (19) which can bescrewed on said pin (16) in opposition to said collar (17).
 6. Theanti-skid system according to claim 5, wherein said sleeve (52) has acircular base from which a series of deformable finger elements (52 a)integrally extend, said elements being able to close together around thebolt (13, 14) of the rim when the sleeve is displaced inside thebell-shaped body (50).
 7. A package, comprising: a system according toclaim 1; and a plurality of sleeves (52) of different sizes able to beengaged with bolts of varying sizes.
 8. A clamping element for ananti-skid system according to claim 1, comprising: a jaw component ableto clamp a bolt and tightening means able to produce a relative movementbetween the jaw component and a containing body shaped so as togradually constrict the jaw body around the bolt, wherein the jaw bodycomprises a plurality of independent clamping blocks (4′, 25′, 35′)which are joined together by resilient means (5′, 10′, 20′, 23′, 30′,42′).
 9. The clamping element for an anti-skid system according to claim8, wherein a bell-shaped body (50) inside which the clamping blocks (4′)slide, has, at least in the inlet mouth portion, a chamfered internalsurface (3′) against which the chamfered external surface of theclamping blocks (4′, 35′) slides.
 10. The clamping element for ananti-skid system according to claim 8, wherein said resilient means arecompression springs (5′) arranged circumferentially between the adjacentsurfaces of said clamping blocks (4′).
 11. The clamping element for ananti-skid system according to claim 8, wherein said resilient means arepieces of rubber or synthetic material (10′) fixed by means of bonding,vulcanization or mechanically onto the opposite surfaces of the adjacentclamping blocks.
 12. The clamping element for an anti-skid systemaccording to claim 8, wherein said resilient means consist of anelastic-washer retaining spring (20′) engaged in slits (21′) formed inthe internal portion of the clamping blocks (4′), the washer exerting apre-compressive force tending to displace the clamping blocks (4′) awayfrom each other.
 13. The clamping element for an anti-skid systemaccording to claim 8, wherein said resilient means consist of aresilient expansion ring (23′) arranged in a groove formed in theinternal surface of the external portion of the clamping blocks (4′).14. The clamping element for an anti-skid system according to claim 8,wherein said resilient means comprise an O-ring (42′) arranged in theinternal portion of the clamping blocks (35′), said blocks (35′) restingon an internal washer (36′).
 15. The clamping element for an anti-skidsystem according to claim 8, wherein said clamping blocks (41, 25′) havean external end which is step-shaped.
 16. The clamping element for ananti-skid system according to claim 15, wherein said clamping blocks(4′) have an external end with several adjacent faces having differentinclinations.
 17. The clamping element for an anti-skid system accordingto claim 8, wherein said tightening means comprise a shank (9′) engagedwith said clamping blocks (4′, 25′, 35′), passing through a supportcollar (17) and translation driven by an operating member (19) acting inopposition to said collar.